Tektronix RSA6100A Series, Help Manual

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General Signal Viewing > DPX Spectrum DPX Primer
Figure 20. DPX spectrum display of WLAN and Bluetooth signals, with a marker on the highest signal.
The “Marker to Peak” function was used to fi nd the peak signal recorded in the display. The marker
readout in the upper left corner of Figure 20 shows the Density, Amplitude, and Frequency for the
pixel you selected with the marker. By adding additional markers, you can measure the signal density
differences between multiple signals of interest.
Marker Peak Search in the DPX Bitmap
Markers on the DPX bitmap can search for peaks, similar to marker peak searching on spectrum line
traces. For a human, it is pretty easy to discern “signals” in the bitmap picture. Your brain intuitively
identi
fi es strings of contiguous bright pixels. This isn’t so easy for a computer. The fi rst thing the RSA
must do for any peak search is analyze pixel density values to identify apparent signals. Then it can sift
through these density peaks for the amplitude peaks you want to
fi nd.
Z-axis density values for the pixels in each column of the bitmap are internally converted into histograms
to
fi nd density peaks indicating the presence of signals. Table 2 shows the fi ve middle columns from
the example grid we used to illustrate density measurements in a previous section (Figure 19). The
density values for each pixel in the middle, highlighted column are plotted on the y axis in the bar chart in
Figure 21. The bar chart x axis is bitmap row number, numbering from the top of the table.
Table 3: Bitmap section showing density values.
0% 0% 0% 0% 0%
0% 0% 8% 0% 0%
0% 0% 12% 0% 0%
0% 0% 26% 0% 0%
0% 0% 36% 0% 0%
0% 2% 6% 2% 0%
4% 8% 0% 8% 0%
86% 82% 4% 76% 12%
RSA6100A Series Real-Time Spectrum Analyzers Help
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